Apple iPhone X display: how big is it, really?

The Apple iPhone X has a 5.8" screen... except it doesn't. You can see on the official site that the 5.8" measurement is for a rectangular screen while the X has rounded corners. But that's a minor quibble, the bigger issue is that there's a cutout at the top of the screen, which limits the usable area. The aspect ratio of the new Super Retina Display is 19.5:9, wider than even Samsung's 18.5:9 (LG and Xiaomi use 18:9). But again, the cutout means you get a small screen that you can practically use. In fact, ignoring the top portion leaves a screen that's just about 18.5:9 in aspect...